1. Field of the Invention
The present invention relates to a pushbutton switch for use in an operating portion of various kinds of electronic apparatus such as a mobile phone, a personal digital assistant (PDA), a car navigation device, or a car audio device, and to a key sheet for the pushbutton switch. In particular, the present invention relates to a pushbutton switch used with a plurality of key tops being exposed to an outside through an operation opening formed in a casing of the electronic apparatus, and to a key sheet for the pushbutton switch.
2. Description of the Related Art
There is known a pushbutton switch adopting a key sheet having a plurality of key tops serving as input keys for the electronic apparatus such as a mobile phone or a PDA. A key sheet 1 according to a related art as disclosed, for example, in JP 2003-323827 A has a structure in which key tops 2 are fixed to a surface constituting an operation surface of a base material film 3 as shown in FIG. 13. The base material film 3 has flexibility according to depressing of the key tops 2 and a repulsive force for restoring the key tops 2 to their original positions when the depression is released. The plurality of key tops 2 are fixed to the base material film 3 through intermediation of adhesive layers 4 in a state where the key tops 2 are independent of each other. As described above, the plurality of key tops 2 can be arranged, and elastic restoration can be achieved only by means of the base material film 3, thereby realizing the small and thin key sheet 1 suitable for a small electronic apparatus.
There is a problem with the key sheet 1, in that, in a case where intervals between the key tops 2 are narrowed, when depressing one of the key tops 2, the key tops 2 adjacent thereto are moved in conjunction therewith, thereby causing an erroneous input, or the key tops 2 adjacent thereto tend to move in conjunction (interfere) therewith, to thereby increase a depressing operation load, making the depressing operation difficult.